Ergometer

ABSTRACT

An electrical ergometer capable of imposing measurable work loads on the user&#39;&#39;s muscles for medical and/or physical therapy purposes. The ergometer includes a torque motor with a plurality of controllable feedback loops for causing the motor to develop different types of easily adjustable forces as it is driven by the user.

United States Patent 3.057192 lO/l962 Huffman etal.

Inventor William E. Thornton 513i Lancelot Drive, San Antonio, Tex.78218 Appl No 844,417 Filed July 24, 1969 Patented June 29, 1971ERGOMETER l0 Claims, 7 Drawing Figs.

US. Cl 73/379 R, 73/ l 33 int. Cl G0ll 5/02 Field of Search 73/l 33,379; 272/73, 79

References Cited UNITED STATES PATENTS 3.092994 6/1963 Moller 73/134'3,375,717 4/1968 lmpellizzeriertal 73/379 3,442,131 5/1969 Leyten .1 73379 2,784,59l 3/1957 Shoor 73/379 FOREIGN PATENTS 475,603 7/1951 Canada272/79 Primary Examiner-Charles A. Ruehl Anorney.lessup & BeecherABSTRACT: An electrical ergometer capable of imposing measurable workloads on the users muscles for medical and/or physical therapy purposes.The ergometer includes a torque motor with a plurality of controllablefeedback loops for causing the motor to develop different types ofeasily adjustable forces as it is driven by the user.

PAlENIEnJuuzelsn 3589.193

SHEET 1 [1F 3 Mam ERGOMIETIEIR BACKGROUND OF THE INVENTION There is awide variety of different types of such ergometers known to the art, themost common type being the externally powered tread mill, as well asunits incorporating various types of weights, and the bicycle or pedaltype of ergometer.

The usual prior art ergometer exhibits certain deficiencies. The mostserious shortcoming is the fact that the forces presented to the musclesare not properly defined. It is known, for example, that the efliciency"of a muscle is directly related to the nature of the load imposed on it.For example, a large pure resistance force rapidly tires the muscle.

Since a frequent present day medical use of the ergometer is to achievehigh physiological workloads for prolonged periods, it is essential thatthe ergometer be a type which may be operated for such prolonged periodwithout excessively tiring the patient. A feature of the ergometer ofthe present invention is that it can be used without excessive tiringfor prolonged periods, so as to improve the efiiciency of thecardiovascular system, a procedure known to the medical art ascardio-vascular conditioning.

It has been found that in order to maintain a relatively large workloadon the patient for a prolonged period, as required, the muscles must becoupled to a load which will not tire them rapidly. The types andmagnitudes of the forces applied to the muscles then become critical. Ithas also been found, in a manner analogous to mechanical engines, thatthe muscles require an inertial flywheel effect in some minimum ratio toother forces in order for them to function efiiciently.

Specifically, the electrical ergometer of the present invention isparticularly advantageous in that the various forces may be appliedseparately to the muscles in any desired magnitude in order to studymuscle action. In addition, improved controls and instrumentation mayeasily be provided in conjunction with the electrical ergometer of thepresent invention to create, sense, display and record, rapid changes inforces, powers and work, as will be described.

The type of forces that may be applied to the muscles of the user by theimproved ergometer of the invention may include the following:

Where:

F is a first type of force X is the displacement K is a constant.

The first type of force F is exemplified by gravitational force orweight. In this case, X will be the vertical displacement of the weightabove its resting position. It should be noted that the force F isalways mixed with inertia in nature.

F,=M A (2) Where:

F is a second type of force M is a mass A is acceleration. The secondtype of force is inertial force and is rarely encountered in pure form,except in freely falling bodies.

Where:

F is a third type of force R is resistance V is velocity n is a powerdepending on the source.

The third force may be considered a family of forces depending upon thevalue of n. The value ofn may typically vary from F2 in viscous dragtype of devices; through n=1 in some types of eddy-current brakes, to n=X in sliding friction after a starting transient.

Where:

F is a further type of force K is a constant X is a constant.

This latter force F, is a spring force and is rarely encountered innature.

As mentioned previously herein, the improved ergometer of the inventionis constructed so that a variety of different forces, such as thosedescribed above, may be exerted on the muscles of the user, each in acontrolled manner, so that any desired force balance may be achieved.The actual mechanisms embodying the invention may be of the linear type,or may be of the pedal type, as mentioned above.

BRIEF DESCRIPTION OF THE DRAWINGS FIGS. 1, 2, 3, 4A and 4B are schematicrepresentations of instrumentalities by which the various types offorces described above may be exerted on the :muscles of the user;

FIG. 5 is an electrical diagram, in conjunction with certain elements,and illustrating appropriate feedback loops for a torque motor so as toachieve the different types of forces developed in the electricalergometer of the present invention; and

FIG. 6 is a circuit by which the various analogs of force, velocity,displacement, power and work, for example, are produced for recordingpurposes.

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENT As mentioned above,FIGS. l-3, 4A and 4B are schematic representations of elementary meansfor achieving the forces described above. For example, with respect toequation (I i.e., F,=K, this force may be achieved by constant forcesprings, such as the illustrated Negator spring assembly 10 in FIG. II.

An elastic flat and set spring 11 is wound on a reel 12, and the end ofthe spring is coupled to a second reel 14. The second reel is mounted ona shaft 16 with a pulley 18. Then, as a force F is applied to a belt 20,for example, wrapped around the pulley 18, the resulting rotation of thepulley causes the shaft 16 to rotate which, in turn, rotates the reel14. When the reel 14 is rotated, it is resisted by the elastic set ofthe spring 111. The magnitude of the constant force F may be controlledby the spring size, or by varying the radii of the reels 12 and 14, andofthc pulley 18.

The second force, as represented by F =M A in equation (2), isrepresented in FIG. 2 by a flywheel 30 which is mounted for rotation ona shaft 32, and which includes a pulley 34 on the shaft. Then, when theforce F is applied to a belt 36 around the pulley, the rotation of thepulley causes the flywheel to rotate so as to obtain a torque which isequal to the moment of inertia of the flywheel l multiplied by itsangular acceleration A simple mass supported on a low friction supportcould be used to achieve the force of equation (2), but it is simpler touse rotating masses, which may be mounted on ball or other low frictionbearings, and subsequently translating the resulting torques into linearforces through a pulley and belt assembly, such as described above. Themagnitude of the force F may be controlled by selecting the mass andconfiguration of the flywheel 30, by varying its mass distribution or byselecting different radii for the pulley 34, or even by using a geararrangement.

The force F;, of equation (3) may be produced by the eddycurrent brake40 illustrated in FIG. 3. This particular eddycurrent brake is a Faradaydisc arrangement, and it comprises a highly electrically conductive disc42 which is composed for example, of an appropriate nonmagneticmaterial, such as copper, aluminum or the like, and which is mounted forrotation within a U-shaped permanent magnet 44. The resulting force F=RXV" which, in this case is F,-,=RXV, may be conveniently developed bthe assembly shown in FIG. 3.

As before, a pulley 46 is mounted on a shaft 48 with the disc 42, sothat the torque may be converted to the linear force F by means of anappropriate strap 50 which is wrapped around the pulley.

The magnitude of the force F, may be adjusted by selecting the strengthof the U-shaped permanent magnet 44, or by relative positioning of thepoles, or by varying the gap between its poles. Also, the magnitude ofthe force is a function of the speed of the disc 42 and of itsconfiguration.

. The force F,=K, X set forth in equation (4) may be.

generated by a simple linear spring 52 such as shown in FIG. 4A, or by acoiled spring 54, such as shown in FIG. 4B. In the latter instance, thecoil spring 54 exerts an angular force on a shaft 56, and a pulley 58 ismounted on the shaft. A belt 60 is wrapped around the pulley, so thatthe force F, is developed as the belt is pulled so as to rotate thepulley 58 and the shaft 56. Magnitude of this latter force I" may bedetermined by the spring constants, or by the pulley ratio in FIG. 48.

Although, as mentioned-above, the mechanical ergometers described in theprior art are simple and reliable, and although they are self-containedunits, they do not possess any high degree of flexibility insofar as thesetting and adjustment of the various types of forces are concerned. Forresearch purposes, for example, the electrical crgometer of the presentinvention, an embodiment of which is shown in FIGS. 5 and 6, has certainadvantages.

For example, torque motors are rotary devices which have an outputtorque directly proportional to input current, with a sine wave responsewhich is tlat to 8-10 seconds or less. Furthermore, torque motors havean appreciable torque at reasonable size and currents, and are capableof providing useful loads for crgometer purposes without the requirementfor large gear ratios.

For that reason, the torque motor is used as a component of theembodiment of the electrical crgometer shown in FIG. 5. By means ofappropriate feedback loops, as will be described, in a closed servosystem, the various forces described above may be simulated. Also, themagnitude of the individual forces may be readily controlledelectrically.

The electrical crgometer shown in FIG. 5, for example, includes a torquemotor 10 which, for example, has a pulley 12 mounted on its drive shaft14, the pulley being driven by a pedal assembly 16 which comprises afurther pulley I8 coupled to the pulley 12 by means of a belt 20. Thepulley 18 is rotated by pedals 22, the assembly 16 being mounted in anappropriate frame, as is the torque motor 10 and its pulley 12. Thepulleys l2 and 18 may be toothed, and the belt 20 may be toothed for amore positive drive.

A linear tachometer goneratorfll) is mechanically coupled to the torquemotor 10, and the tachometer develops a signal E which may be consideredto be equal to the angular velocity of the torque motor t'u. The torquemotor 10 is energized by a constant current generator 32 which providesa constant current through the torque motor 10 for a given feedbackload, regardless of speed. The current generator 32 cnergizes the torquemotor and causes it to tend to turn in one direction. When the useroperates the pedals 20, he turns the torque motor In the oppositedirection, causing the linear tachometer generator 30 to generate thesignal E.

A voltage 5,, is applied to the the current generator 32, and thisvoltage is the sum of three separate voltages E,, E and E,,, the lattervoltages being intended to represent the various forces described above.For example, the voltage E, is developed at the output of an operationalamplifier 34, whose input is connected to a constant voltage source E,,.

The operational amplifier 34 is shunted by a potentiometer R,, and thispotentiometer may be adjusted, so that the voltage E, has any desiredconstant value, with the operational amplifior 34 providing a lowimpedance source for the constant voltage. Also, the constant voltage E,may be set to any desired value, by an appropriate adjustment of thepotentiometer R,. The voltage E, is the electrical analog of the forceF, of equation (I) which is a constant force. Also, this force may haveany desired value, as determined by the setting of the potentiometer R,.

The system of FIG. 5 also includes a multiple channel feedback loop. Afirst channel in the feedback loop includes an operational amplifier 36which is shunted by a potentiometer R and which is connected directly tothe output of the linear tachometer generator 30. The operationalamplifier 36 produces the voltage E which is the electrical analog ofthe force F of equation(3). That is, the voltage E varies with thevelocity'tb as represented by E applied to the input of the operationalamplifier 36. Therefore, the electrical analog of the force F, is alsoapplied to the input of the current generator 32.

The feedback loop includes a second channel incorporating a firstoperational amplifier 38 having its input coupled to the output of thegenerator 30 through a capacitor 40, and shunted by a resistor 42. Theoperational amplifier 38 produces a voltage E" at its output which, dueto the differentiating action of the circuit element 40 and 42 is equalto da'i/dt which equals This latter voltage is translated by a secondoperational amplifier 44, the latter amplifier being shunted by apotentiometer R,,. The operational amplifier 44 develops a voltage E,,at its output, which is the electrical analog of the force F of equation(2). That is, the voltage E is proportional to the acceleration iii ofthe torque motor 10.

The constant current generator 32 is activated by the voltage E,,, whichis the sum of the voltages E,, E and E,,. This latter generator,therefore, causes the torque motor to exhibit forces when the pedals 20are operated, and which are of different types, as represented by theequations (2), (3) and (4) set forth previously herein. Also, merely byadjusting the potentiometers R,, R and R,,, the different types offorces may have any desired magnitude.

Specifically, the rate of rotation of the torque motor 10 is convertedto an analog voltage E which is proportional to the angular velocity ofthe torque motor, and which becomes the signal which drives the inertiaand resistance legs of the force generator. Specifically, the outputtorque T of the torque motor 10 is converted into a force R, which isrelated as follows:

The foregoing is analogous to:

The spring force of FIGS. 4A and 4B is not included in the electricalcrgometer of FIG. 5 because that force is seldom used. However, it couldbe added if so desired. Also, the resistance force could be changed to aviscous resistance RV for example, by adding a multiplier for thevoltage E,,. Since the potentiometers R,, R, and R,, may be easilyadjusted to any selected value, the magnitudes of the various voltagesE,, E and E,, may be readily controlled and varied.

To make full use of the electrical crgometer of FIG. 5, for example, arecord should be made of the instantaneous forces, displacements, powerand work performed by the user. In mechanical devices, such as thosedescribed in the prior art, these records may be obtained, for example,from a strain gauge, and if the forces are converted to linear motion,they may be obtained by a velocity pickup. In the electrical er gometerof FIG. 5, for example, the desired records may be obtained in asimplified manner, and by a simple network, such as shown in FIG. 6.

In the circuit of FIG. 6, only the elementary analog computation isrequired to yield the needed analogs of force, velocity, displacement,power and work, for recording purposes. The simplified versions for thepedal crgometer, such as shown in FIG. 5, for example, can use muchsimpler instruments since only averages are important. For example, asimple tachometer, and a Vceder Root counter may be used with a gauge toindicate the various loadings.

As shown in FIG. 6, for example, the pedal drive for the torque motor 10may be replaced by a drum and a handle I02 which is coupled to the drumby a line 104 reeled about the drum. The motor then is driven by theuser drawing the handle, with an appropriate ratchet arrangement beingprovided (not shown) so that reciprocally pulling the handle 102 causesthe motor to achieve a certain speed with a particular loading, asestablished by setting the potentiometers R R and R in the circuit ofFIG. 5. A strain gauge 106 is provided in the line 104, so that avoltage may be developed which is proportional to the force exerted. itwill be appreciated, of course, that a similar arrangement may beprovided in conjunction with the pedal assembly of FIG. 5, so that asimilar voltage may be generated which is proportional to the voltagedeveloped by the pedal assembly. The resulting voltage E, from thestrain gauge 106 is amplified in an amplifier 108, so that a voltage E lis developed which is proportional to force. It will be appreciated,therefore, that a suitably calibrated instrument may be connected to theoutput terminal 110, and the instrument may designate force directly.

In addition, the output E from the tachometer generator 30, which isproportional to velocity rb may be applied to an output terminal 112,and an appropriately calibrated instrument, connected to the outputterminal would provide a direct indication of velocity.

The voltage E which is proportional to velocity (b may be integrated ina network including an operationalamplifier 114, and an integratingnetwork made up of a capacitor 116 at its input, and a shunting resistor118, to provide an output voltage E". The latter voltage may be appliedto an output terminal 120, and a suitable voltmeter, or recorder,connected to the output terminal 120 may be calibrated to provide adirect indication of acceleration.

Likewise, the voltage E may be applied to an operational amplifier 122and associated differentiating network including a resistor 124 at theinput to the differential amplifier, and a shunting capacitor 126, sothat a voltage E V is produced. The latter voltage may be applied to anoutput terminal 128, so that an appropriately calibrated meter connectedto the output terminal may provide a direct reading of displacement.

A multiplier circuit 130 of any known type may be connected into thecircuit to receive the voltages E and E so as to produce a voltage E"representative of force multiplied by velocity which equals power. Thelatter voltage may be applied to an output terminal 132, so that thepower developed may be directly indicated by an appropriate meter, orrecorder, connected to that output terminal.

The voltage E" may be applied through a resistor 134 to an operationalamplifier 136, the operational amplifier being shunted by a capacitor138 to form an integrating network, so that a voltage E applied to anoutput terminal 140 is a direct indication of the work done, and thisvalue may be directly indicated by a suitably calibrated voltmeter, orrecorder, connected to the output terminal 140.

The electrical ergometer of the present invention, therefore, is mostadvantageous in that the desired forces may be simulated with anydesired magnitude by a simple potentiometer adjustment. Moreover, theresulting voltages developed within the system itself may be used toprovide appropriate instrumentation voltages, so that simple meters maybe used to display on a direct basis, and by suitable calibrations, thevarious parameters described in FIG. 6.

What I claim is:

1. An electric ergometer for imposing measurable work loads on themuscles of a user, including: an electric motor having a drive shaft;circuit means for energizing said motor so as to cause said drive shaftto tend to rotate in a particular direction; manually operable meansmechanically coupled to said drive shaft for rotating said drive shaftin the opposite direction; electric generating means coupled to saidmotor for generating an electric signal having a value related to theangular velocity of said drive shaft in said opposite direction; andelectric feedback circuit means connected to said generating means andto said energizing circuit means for creating a force in said motoropposing such rotation in said opposite direction and which is afunction ofsaid angular velocity.

2. The electric ergometer defined in claim 1, and in which said electricfeedback circuit means includes a network for differentiating the signalfrom said electric generating means so as to create an additional forcein said motor opposing such rotation in said opposite direction andwhich is a function of the angular acceleration of the drive shaft insaid opposite direction.

3. The electric ergometer defined in claim 1 and which includes anetwork for introducing a constant signal to said energizing circuitmeans for creating a constant additional force in said motor opposingsuch rotation in said opposite direction.

4. The electric ergometer defined in claim 3 and which includesadjustable potentiometers in said last-named network and in saidfeedback circuit means for setting the aforesaid forces created in saidmotor to predetermined values.

5. The electric ergometer defined in claim 1 in which said manuallyoperable means includes a rotatable pedal assembly.

6. The electric ergometer defined in claim 1 in which said manuallyoperable means includes a linearly movable assembly.

7. The electric ergometer defined in claim 1 in which said manuallyoperable means includes means developing an electric signalrepresentative of the force exerted on said manually operable means; andcircuitry coupled to said last-named means for developing an electricinstrumentation signal indicative of said force.

8. The combination defined in claim 7 in which said circuitry includes anetwork coupled to said electric generating means for developing furtherinstrumentation signals indicative of the work performed by the user.

9. The electric ergometer defined in claim 1 and which includescircuitry coupled to said electric generating means for developinginstrumentation signals representative of the an gular velocity of saiddrive shaft.

10. The combination defined in claim 9 in which said lastnamed circuitryfurther develops an instrumentation signal representative of the angularacceleration of said drive shaft.

1. An electric ergometer for imposing measurable work loads on themuscles of a user, including: an electric motor having a drive shaft;circuit means for energizing said motor so as to cause said drive shaftto tend to rotate in a particular direction; manually operable meansmechanically coupled to said drive shaft for rotating said drive shaftin the opposite direction; electric generating means coupled to saidmotor for generating an electric signal having a value related to theangular velocity of said drive shaft in said opposite direction; andelectric feedback circuit means connected to said generating means andto said energizing circuit means for creating a force in said motoropposing such rotation in said opposite direction and which is afunction of said angular velocity.
 2. The electric ergometer defined inclaim 1, and in which said electric feedback circuit means includes anetwork for differentiating the signal from said electric generatingmeans so as to create an additional force in said motor opposing suchrotation in said opposite direction and which is a function of theangular acceleration of the drive shaft in said opposite direction. 3.The electric ergometer defined in claim 1 and which includes a networkfor introducing a constant signal to said energizing circuit means forcreating a constant additional force in said motor opposing suchrotation in said opposite direction.
 4. The electric ergometer definedin claim 3 and which includes adjustable potentiometers in saidlast-named network and in said feedback circuit means for setting theaforesaid forces created in said motor to predetermined values.
 5. Theelectric ergometer defined in claim 1 in which said manually operablemeans includes a rotatable pedal assembly.
 6. The electric ergometerdefined in claim 1 in which said manually operable means includes alinearly movable assembly.
 7. The electric ergometer defined in claim 1in which said manually operable means includes means developing anelectric signal representative of the force exerted on said manuallyoperable means; and circuitry coupled to said last-named means fordeveloping an electric instrumentation signal indicative of said force.8. The combination defined in claim 7 in which said circuitry includes anetwork coupled to said electric generating means for developing furtherinstrumentation signals indicative of the work performed by the user. 9.The electric ergometer defined in claim 1 and which includes cirCuitrycoupled to said electric generating means for developing instrumentationsignals representative of the angular velocity of said drive shaft. 10.The combination defined in claim 9 in which said last-named circuitryfurther develops an instrumentation signal representative of the angularacceleration of said drive shaft.